The present invention relates to a frequency generating circuit and to a receiving apparatus comprising such a frequency generating circuit. An example of the receiving apparatus is a digital paging receiver.
In the present specification the term "receiving apparatus" is to be understood to cover at least the receiving section of a transceiver apparatus which may comprise an answer back paging apparatus or a cordless and/or cellular telephone.
Many different types of frequency generating circuits are known in the art. For example temperature controlled crystal oscillators are known and normally require a high tolerance crystal to provide frequency stability. The more accurately a crystal is cut the greater its cost. It is known to place crystals in temperature controlled ovens in order to stabilise their frequencies. Drawbacks to using an oven in radio apparatus, especially a portable radio apparatus, are space and power consumption consideration.
DE 44 03 1241 A1 discloses a radio clock circuit in which dedicated radio timing signals are used to synchronise a quartz oscillator in clock circuit.
Frequency synthesiser circuits are also well known and generally require a highly stable reference oscillator from which the desired frequency is obtained by a division operation.